Method and apparatus for fiberscope

ABSTRACT

The disclosure generally relates to a method and apparatus for a fiberscope. In one embodiment, the disclosure relates to a chemical imaging fiberscope for imaging and collecting optical spectra from a sample having at least one illumination fiber for transmitting light from a first an a second light source to a distal end of a fiberscope; a dichroic mirror disposed at said distal end of the fiberscope such that light from said first light source passes substantially straight through said mirror and light of a predetermined wavelength from said second light source is substantially reflected by said mirror toward said sample to thereby illuminate said sample; and at least one collection fiber for receiving light from said illuminated sample and transmitting the received light to an optical device.

The instant application claims the filing-date benefit of applicationSer. Nos. 10/934,885 and 10/935,423, filed Sep. 3, 2004 and Sep. 7,2004, respectively. Each of said applications claims the filing datebenefit of application Ser. No. 09/619,371 (now U.S. Pat. No. 6,788,860)filed Jul. 19, 2000, which itself claims the filing-date benefit ofProvisional Application No. 60/144,518 filed Jul. 19, 1999. Reference isalso made to application Ser. Nos. 09/976,391 (now U.S. Pat. No.6,734,962) and Ser. No. 09/064,347 (now U.S. Pat. No. 6,002,476) whichare assigned to the assignee of the instant application. Thespecifications of each of the above-identified applications isincorporated herein in its entirety for background information.

BACKGROUND

Chemical imaging combines optical spectroscopy and digital imaging forthe molecular-specific analysis of materials. Raman, visible, nearinfrared (VIS/NIR) and Fluorescence chemical imaging have traditionallybeen performed in laboratory settings using research-grade lightmicroscope technology as the image gathering platform. However, chemicalimaging is applicable to in situ industrial process monitoring and invivo clinical analysis. The application of chemical imaging outside theresearch laboratory has been limited by the lack of availability ofstable imaging platforms that are compatible with the physical demandsof industrial process monitoring and clinical environments. Bothindustrial and clinical settings often require compact, lightweightinstrumentation suitable for the examination of remote areas that areinaccessible to conventional chemical imaging instrumentation andinvolve harsh chemicals in hostile areas. In addition, for in vivocardio-vascular clinical applications, the presence of blood and bodilyfluids limits the viewing, identification and ability to perform in vivooptical measurements of suspect areas.

Raman spectroscopy is one of the analytical technique that is broadlyapplicable and can be used for chemical imaging. Among its manydesirable characteristics, Raman spectroscopy is compatible with samplesin aqueous environments and can be performed on samples undergoinglittle or no sample preparation. The technique is particularlyattractive for remote analysis via the use of optical fibers. Byemploying optical fibers for light delivery and collection the lightsource and light detector can be physically separated from the sample.This remote attribute is particularly valuable in sensing and analysisof samples found in industrial process environments and living subjects.

In a typical fiber-optic based Raman analysis configuration, one or moreillumination fiber-optics deliver light from a light source (typically alaser) through a laser bandpass optical filter and onto a sample. Thelaser bandpass filter allows only the laser wavelength to pass whilerejecting all other wavelengths. This purpose of the bandpass filter isto eliminate undesired wavelengths of light from reaching the sample.Upon interaction with the sample, much of the laser light is scatteredat the same wavelength as the laser. However, a small portion of thescattered light (1 in 1 million scattered photons on average) isscattered at wavelengths different from the laser wavelength. Thisphenomenon is known as Raman scattering. The collective wavelengthsgenerated from Raman scattering from a sample are unique to thechemistry of that sample. The unique wavelengths provide a fingerprintfor the material and are graphically represented in the form of aspectrum. The Raman scattered light generated by the laser/sampleinteraction is then gathered using collection optics which directs thelight through laser rejection filter which eliminates the laser light,allowing only Raman light to be transmitted. The transmitted light isthen coupled to a detection system via one or more collectionfiber-optics.

Previously described Raman fiber optic probe devices have severallimitations. First, current fiber-optic-based Raman probes are sensitiveto environmental variability. These devices often fail to functionproperly when the probe is subjected to hot, humid and/or corrosiveenvironments. Several fundamental differences from current devices havebeen incorporated into the chemical imaging fiberscope design describedhere that address the environmental sensitivity issue. First, an outerjacket (or housing) that is mechanically rugged and resistant to varyingtemperatures and high humidity has been incorporated into the fiberscopedesign. Second, an optically transparent window that withstands harshoperating environment has been built into the probe at thefiberscope/sample interface. Normally, incorporation of a window into aprobe would introduce a significant engineering problem. As emittedillumination light passes through the window and onto the sample, aportion of this light is back reflected by the window's inner and outersurfaces. In the prior art, this undesired back reflected light isinadvertently introduced into the collection fibers along with thedesired Raman scattered light. The back reflected light corrupts thequality of the analysis. This problem is addressed in the current designby careful engineering of the aperture of the collection bundle takinginto account the numerical apertures (NA) associated with the collectionbundle fibers and collection lenses.

Previous probe designs are also inadequate because of the environmentalsensitivity of the spectral filters that are employed in the devices.The chemical imaging fiberscope design of the current disclosure relieson spectral filter technologies that are remarkably immune totemperature and humidity. Past spectral filters have traditionally beenfabricated using conventional thin film dielectric filter technologywhich are susceptible to temperature and humidity induced degradation inthe filter spectral performance. The spectral filters described in thepresent disclosure employ highly uniform, metal oxide thin film coatingmaterial such as SiO₂ which exhibits a temperature dependent spectralband shift coefficient an order of magnitude less than conventionalfilter materials. The improved quality and temperature drift performanceof metal oxide filters imparts dramatically improved environmentalstability and improved Raman performance under extreme conditions oftemperature and humidity.

Another limitation of current probe technologies is that none combinethe three basic functions of the chemical imaging fiberscope: (1) videoinspection; (2) spectral analysis; and (3) chemical image analysis in anintegrated, compact device.

Raman chemical imaging integrates the molecular analysis capabilities ofRaman spectroscopy with image acquisition through the use ofelectronically tunable imaging spectrometers. In Raman chemical imaging,scattered Raman light is shifted in wavelength from the wavelength ofthe illuminating light. For example, Raman illumination at 532 nm canexcite molecular vibrations in the sample at for example, 4000 cm⁻¹ toproduce scatter Raman light at lower and higher wavelengths of 439.3 nmand 647.5 nm, respectively. The Raman wavelength can be in the range of−4000–4000 cm⁻¹. This produced Raman features 4000 cm⁻¹ above theilluminating wavelength. Several imaging spectrometers have beenemployed for Raman chemical imaging, including acousto-optical tunablefilters (AOTFs) and liquid crystal tunable filters (LCTFs). For Ramanimaging, LCTFs are clearly the instrument of choice based on thefollowing demonstrated figures of merit: spatial resolving power (250nm); spectral resolving power (<0.1 cm⁻¹); large clear aperture (20 mm);and free spectral range (0–4000 cm⁻¹). LCTF's can also be designed bythose skilled in the art to operate over different ranges of detectionwavelengths that depend on the application from, for example, 400–720nm, 650–1100 nm, 850–1800 nm or 1200–2400 nm. AOTFs and LCTFs arecompetitive technologies. AOTFs suffer from image artifacts andinstability when subjected to temperature changes.

Under normal Raman imaging operation, LCTFs allow Raman images ofsamples to be recorded at discrete wavelengths (energies). A spectrum isgenerated corresponding to thousands of spatial locations at the samplesurface by tuning the LCTF over a range of wavelengths and collectingimages systemically. Contract is generated in the images based on therelative amounts of Raman scatter or other optical phenomena such asluminescence that is generated by the different species locatedthroughout the sample. Since a spectrum is generated for each pixellocation, chemometric analysis tools such as Cosine Correlation Analysis(CCA), Principle Component Analysis (PCA) and Multivariate CurveResolution (MCR) are applied to the image data to extract pertinentinformation.

Chemical imaging can be performed not only in a scattering mode at highresolution as done for Raman chemical imaging using laser illumination,but it can also be conducted for broadband incident illumination(wavelength>10 cm⁻¹) at corresponding reduced spectral resolution(wavelength>10 cm⁻¹). This broadband illumination and reduced resolutionspectroscopy can be done in the UV wavelength (200–400 nm), VISwavelength (400–780 nm) and NIR wavelength (780–2500 nm) regions tomeasure the optical absorption and emission from the sample. Performingsuch absorption or emission measurements using a fiberscope requiresaddressing many of the same problems as encountered in performing Ramanimaging. The ability to perform combinations of these opticalmeasurements and chemical imaging in the same fiberscope system is alsoan advantage in that enabling different chemical imaging technologies inone platform provides valuable complementary information.

One problem in performing chemical analysis and chemical imaging in thehuman body, such as in for example, in the cardio-vascular system orbody cavities during, for example, endoscopic surgery, is the occurrenceof significant amounts of blood and water at the sample site which bothscatters and absorb light in certain wavelength ranges. Further, thepositioning of a fiberscope probe to perform an in vivo optical analysisrequires accurate steering and viewing thru these body fluids so as todefine regions of interest and accurately position the optical probe atthe region to be sampled. Viewing more than a few millimeters throughblood requires observation at NIR wavelengths. However, such NIRwavelengths are poorly suited for performing Raman scattering orfluorescence measurements.

For example, identification and characterization of vulnerable plaque inthe cardio-vascular system is critically related to Cardio vasculardisease which is a leading cause of deaths in the United Stated. The invivo identification and characterization of plaques in the cardiovascular system requires locating the suspect regions and positioning asampling probe to analyze these regions. Other current methods forcharacterizing vulnerable plaque such as Intra Vascular UltraSound(IVUS) and thermometry (e.g., Volcano Therapuetics, Inc.) map out somephysical properties of the arterial walls to suggest likely areas ofplaques, but are not chemically specific and cannot provide any detailedanalytical information regarding the chemical state or molecularcomposition of these target areas or plaques. Optical imaging toposition a chemical probe in vivo is desirable but problematic andlimited due to the scattering and absorption properties of blood. Whilecertain optical wavelengths in the NIR are known to be more favorablethan others for in vivo viewing of the cardiovascular system, thesewavelengths are not well-suitable for performing highly specificchemical analysis. For example, the Raman scattering cross sections atlonger wavelengths (e.g., NIR) are reduced from VIS wavelengthexcitation by the fourth power of their respective frequencies. The lowcost, high sensitivity Si charge-coupled detectors (“CCD”) used forRaman Chemical imaging also have reduced sensitivity for longerwavelength Raman scattered peaks thereby making it difficult to detectthe very important CH-bond vibrational region.

Thus, there is a need for an apparatus and method to enable long rangeviewing, steering and targeting which is optimal in the NIR as well assubsequent and/or simultaneous chemical imaging of the target area whichis optimal in the visible range. This invention addresses that need.

SUMMARY OF THE DISCLOSURE

In one embodiment, the disclosure relates to a chemical imagingfiberscope for imaging and collecting optical spectra from a samplecomprising at least one illumination fiber for transmitting light from afirst and a second light source to a distal end of a fiberscope; adichroic mirror disposed at said distal end of the fiberscope such thatlight from said first light source passes substantially straight throughsaid mirror and light of a predetermined wavelength from said secondlight source is substantially reflected by said mirror toward saidsample to thereby illuminate said sample; and at least one collectionfiber for receiving light from said illuminated sample and transmittingthe received light to an optical device.

In another embodiment, the disclosure relates to a system for imagingand collecting optical spectra from a sample comprising a near infrared(“NIR”) light source; a laser light source; a fiberscope including atleast one illumination fiber; a dichroic mirror; at least one collectionfiber; and an optical device, wherein said at least one illuminationfiber is operatively connected at a proximate end to said NIR lightsource and said laser light source so as to transmit light from saidlight sources to said dichroic mirror disposed in proximity to a distalend of said illumination fiber and wherein said dichroic mirror allowslight from said NIR light source to pass substantially straight throughsaid mirror and substantially reflects light from said laser lightsource toward said sample to thereby illuminate said sample. The atleast one collection fiber can receive light from said illuminatedsample and transmit the received light to the optical device for imagingand collecting optical spectra and chemical images of the sample.

In still another embodiment, the disclosure relates to a method ofimaging and collecting optical spectra from a sample, the methodcomprising the steps of providing a fiberscope including at least oneillumination fiber operatively connected at a proximal end to a firstlight source and a second light source so as to transmit light from saidfirst and second light sources to a dichroic mirror disposed inproximity to a distal end of the fiberscope; at least one collectionfiber for receiving light from said illuminated sample and transmittingthe received light to an optical device; and a dichroic mirror disposedat the distal end of the fiberscope which allows light from the firstlight source to pass substantially straight through the mirror whilesubstantially reflecting light from the second light source toward thesample to thereby illuminate the sample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of the distal end of the Raman chemicalimaging fiberscope;

FIG. 2 shows a functional flowchart of pathways for light delivery andcollection through the chemical imaging fiberscope;

FIG. 3A is a schematic representation of one embodiment of thedisclosure;

FIG. 3B is a schematic representation of another embodiment of thefiberscope's dichroic probe region;

FIG. 3C is a schematic representation of another embodiment of thefiberscope's dichroic probe region;

FIG. 4 is a schematic representation of a dichroic fiberscope probe inan artery according to one embodiment of the disclosure for evaluatingregions in the arterial wall;

FIGS. 5A and B respectively show the bright field images of the exteriorand interior of a bore hole captured through the chemical imagingfiberscope;

FIG. 6A shows an image of the laser beam projected onto a resolutiontarget images collected through the chemical imaging fiberscope;

FIG. 6B shows an image of the resolution target only for comparison;

FIG. 7A shows the simultaneous transmission of white light and laserlight through the laser delivery fiber optic and laser bandpass filter;

FIG. 7B shows the transmission bandpass through the laser rejectionfilter and coherent imaging bundle;

FIGS. 8A and B show Raman spectra of a sodium nitride pellet and asodium phosphate solution, respectively, captured through the chemicalimaging fiberscope;

FIG. 9 shows Raman spectra of zirconium oxide collected at roomtemperature and at 205° C. through the chemical imaging fiberscopeaccording to one embodiment of the disclosure;

FIGS. 10A and 10B show bright field images of an aspirin tabletcollected through the fiberscope under white illumination conditions;

FIG. 10C shows a Raman spectrum of the aspirin tablet captured from theboxed region in FIG. 9B and collected with a dispersive Ramanspectrometer under Raman spectroscopy conditions;

FIG. 11A shows bright field images of a micro region of a tabletcontaining aspirin collected through the fiberscope under white lightillumination conditions;

FIG. 11B shows a Raman chemical image of the same tablet collectedthrough the fiberscope operating under Raman imaging conditions; and

FIG. 11C shows representative Raman spectra collected through imagingspectrometer of aspirin and excipients.

DETAILED DESCRIPTION

The Raman chemical imaging fiberscope combines in a single platform alaser beam delivery system to irradiate samples for Raman spectroscopy,an incoherent fiber optic bundle to deliver white light illumination anda coherent fiber bundle suitable for Raman spectral collection, Ramanimage collection and digital video collection.

The distal end of the fiberscope is shown in cross-section in FIG. 1.The external housing 10 surrounds the inner core of the fiberscope. Theouter jacket 10 is mechanically rugged and immune to hostile samplingenvironments. The compression tube 23 holds the fibers 18, the filter 24and lens 22 in alignment. At the distal end of the fiberscope is window12. This window is, in one embodiment, composed of quartz, diamond orsapphire and is used as an optically transparent boundary separating thesample environment from the optical components in the probe. In analternative embodiment, the other biocompatible material such asplastics, glass or semiconductors can be used for the opticallytransparent window.

Laser illumination fiber 14 delivers laser illumination to the sample.This light passes through laser bandpass filter 24, which filters outall wavelengths of light other than the specific wavelengths of thelaser light transmitted through laser illumination fiber 14. The laserlight/sample interaction generates Raman scattering. The scattered lightis then collected through the end of the fiberscope. It should be notedthat laser bandpass filter 24 is spatially patterned and has opticalcoatings only on the top portion thereof, such that light exiting laserillumination fiber 14 will be filtered, but scattered light entering theend of the probe will not experience any filtering by laser bandpassfilter 24. The portion of laser bandpass filter 24 which receivesscattered light form the sample and transmits it to image collectionbundle 18 is transparent and performs no filtering function.

After passing, through laser bandpass filter 24, the scattered light isapertured by a spatial filter 28 which acts to restrict the angularfield or view of the subsequent optical system. The scattered light isthen focused by a pair of lenses 22. The light is then passed throughlaser reflection filter 20. This filter effectively filters out lighthaving a wavelength identical to the laser light, which was originallytransmitted onto the sample through laser illumination fiber 14. Afterpassing through filter 20, the light is transmitted back to the imagingapparatus by the image collection bundle 18.

Successful use of the Raman chemical imaging fiberscope depends on theperformance of the spectral filters in humid, elevated-temperatureenvironments. Conventional filters are characterized by the presence ofmicroscale pits and voids. These microstructures absorb water in humidconditions, which cause the thin film matrix to swell and the spectralproperties to change, causing the fiber optic probe to be useless. Inaddition, the coefficients of thermal expansion of traditionaldielectric filter thin films (i.e., ZnS or ZnSe) are relatively large.When exposed to elevated temperatures the traditional filter centerspectral bandpass shifts, rendering them useless unless a mechanism isdevised to rotate the filters and turn them. For example, ZnS has atemperature coefficient of 0.05 nm/° C.

In the preferred embodiment, the filters are metal oxide dielectricfilters. Metal oxide filters have low coefficients of thermal expansionand when exposed to elevated temperature environments the thin filmmaterials comprising the Fabry-Perot cavities do not exhibit grossvariation in thin film thickness. As a consequence, the metal oxidefilters are insensitive to temperature induced spectral changes,primarily peak transmittance. In addition, the metal oxide thin filmcoating is also insensitive to humidity which enhances the filterperformance when exposed to hostile conditions. The metal oxide filtersemploy SiO₂ as the thin film material, which exhibits a temperaturedependent spectral band shift coefficient of about 0.005 nm/° C.

The imaging fiber optic bundles are preferably high temperatureresistant coherent fiber optic bundles, such as those developed bySchott Glass. These bundles have the unique property that the polyamidecladding employed for typical coherent fiber bundles is leached away (inacid bath) leaving an all-glass fiber bundle that is flexible and can beoperated at high temperatures up to about 400° C.

Video imaging of the sample is performed by shining white light on thesample. The white light is transmitted via fibers 26. High qualityimaging optics are employed to provide the ability to visually inspectthe sample area and to obtain Raman chemical images. Collection lenses22 focus an image of the sample on the image collection bundle 18. Thecoherent image collection bundle 18 independently captures white lightand Raman scattered photons from the sample surface. The Raman chemicalimaging fiberscope provides remote real-time video imaging of the samplewhen the white light is directed through the image collection bundle 18to a video CCD. Live video capability assists insertion of thefiberscope and allows Visual inspection of the sample area inpreparation for spectroscopic analysis. White light for video imagingcan be produced by a high power (300 W) Xe lamp.

The Raman scatter is collected through the coherent image collectionbundle 18 used to capture the live video. However, laser rejectionfilter 20 is used to suppress generation of SiO₂ Raman background withinthe image collection bundle 18. As shown in FIG. 2, once collected, theRaman scatter can be diverted in two directions. When sent to adispersive spectrometer, the Raman chemical imaging fiberscope providesconventional Raman spectral information. The Raman scatter can also bedirected through a liquid crystal tunable filter (LCTF) imagingspectrometer onto sensitive digital CCD. Because the Raman image ismaintained through the image collection bundle 18, high quality Ramanchemical images can be collected across the fiberscope field of view.

FIG. 2 shows a functional diagram of the Raman chemical imagingfiberscope system. Laser light illumination and white light videoilluminations are represented by reference numbers 1 and 2 respectively.These lights enter the fiberscope and are transmitted out the end of thescope to the sample. The Raman spectrum 3, the Raman image 4 and thelive video image 5 are transmitted back into the end of the fiberscope.Raman spectrum 3 and Raman image 4 are delivered to processing apparatuswhich effectively displays the desired information, as described above,while live video image 5 is directed to a monitor for viewing by theuser.

FIG. 3A is a schematic representation according to one embodiment of thedisclosure. Referring to FIG. 3A, a system is shown having illuminationfibers 14 receiving photons from various sources identified as S₁, S₂,S₃ . . . S_(n). For example, the first light source can be a nearinfrared (NIR or broadband NIR) while second and third light sources,respectively, can be laser and/or white light. The white light can bevisible VIS (broadband) or ultraviolet UV (broadband). The NIR sourcecan have a wavelength in the range of about 780–2500 nm or 0.78–2.5 μm.In one embodiment, the exemplary apparatus of FIG. 3A may include aswitch (not shown) for alternately connecting any of the sources (S₁ . .. S_(n)) to the at least one of the illumination fibers 14. For example,the switch can connect the first light source to one of the illuminationfibers 14 for guiding the fiberscope through for example an artery tothe sampling position. The switch can also connect the second lightsource to another of illumination fiber 14 for simultaneously orsequentially illuminating the sample or performing spectroscopy.

Illumination fibers 14 can comprise one or more transparent opticalfibers devised to transmit light from one or more sources to sample 35.In one embodiment, plural illumination fibers can be arranged as abundle such that one of the illumination fibers 14 transmits lightexclusively from a first light source to the sample while another of theplural illumination fibers transmits light exclusively from a secondlight source to the sample. According to still another embodiment,illumination fibers 14 and light sources (S₁ . . . S_(n)) can bearranged such that at least one illumination fiber 14 transmits lightfrom the first, second and third light sources to the distal end of thefiber scope. Illumination fibers 14 can include conventional transparentoptical fibers.

Interposed between the distal end of the illumination fibers 14 andsample 35 is dichroic mirror 30. The dichroic mirror can be selected toreflect light of predetermined wavelength while allowing light of otherwavelengths to pass substantially through mirror 30. In other words, inone embodiment dichroic mirror 30 is positioned at the distal end of thefiberscope such that light from a first light source passessubstantially through the mirror while light of a predeterminedwavelength (for example, from the second light source) is substantiallyreflected by the mirror toward the sample in order to illuminate sample35. While the exemplary embodiment of FIG. 3A shows dichroic mirror 30positioned at an angle with respect to housing 10 of the fiberscope, theprinciples of the disclosure are not limited thereto. The dichroicmirror 30 can be selected such that its optical properties would beresistant to temperature and/or humidity changes.

In one embodiment, the predetermined wavelength can be about 670 nm. Thepredetermined wavelength can also be in the range of about 220–1500 nm,500–850 nm or 270–550 nm.

Photons emitted from sample 35 can be collected through collectionfibers 38 and transmitted through one or more spatial filter 28 to anoptical device (not shown). It should be noted that laser bandpassfilter 24 is spatially patterned and has optical coatings only on thetop portion thereof, such that light going into the fibers 38 is notfiltered. Spatial aperture 28, lens 22 and spectral filter 20 areinterposed between sample 35 and collection fibers 38. Spatial filter 28can be used to reduce unwanted light from entering the fibers 38. Lens22 can focus light into collection fibers 38. Spectral filter 20 can beany conventional bandpass filter capable of rejecting light of anunwanted wavelength. Filters 20 can be configured such that the photonsreceived by collection fibers 38 can have a wavelength in the range ofabout 500 to 680 micrometers. In one embodiment, spectral filter 20 isused to reject light having a wavelength substantially similar to thewavelength of the light emitted by the laser light source while allowinglights having a different wavelength to pass through.

Lens 22 are also interposed between sample 35 and collection fibers 38.Lens 22 can be a conventional optical lens for gathering and/or focusinglight. While the exemplary configuration of FIG. 3A shows a particularorder and arrangement for spatial filter 28, spectral filters 24 and 20and lens 22, the principles of the disclosure are not limited thereto.For example, a plurality of optical devices can be assembled to functionas a spatial or spectral filter. Moreover, the utilization of each andall of these elements is optional and may not be necessary for a desiredoutcome.

In one embodiment of the disclosure photons scattered, reflected,refracted or fluoresced by sample 35 are transmitted by collectionfibers 38 to an optical device (not shown). The optical device can beselected according to a desired application for the system. For example,the optical device can be a Raman chemical imaging spectrometer anddetector. The optical device can be further coupled to a controller, adisplay device or a recording medium.

The exemplary system shown in FIG. 3A also includes external housing 10having window 12 at its distal end. Window 12 may include quartz,diamond or sapphire. In some cases window 12 may also include plastic,glass or a semiconductor. In another embodiment, window 12 may include afirst portion which is spatially patterned for the light from said firstlight source and a second portion which is transparent for the lightfrom the second source.

In an exemplary application, the fiberscope of FIG. 3A can be configuredfor collecting Raman spectra from a sample by using NIR as S₁, a laserlight as S₂ and white light as S₃. The fiberscope can include at leastone illuminator fiber, a dichroic mirror 30, a collection fiber bundle38 and an optical device (not shown). The illumination fiber 32 can beoptically coupled, at a proximal end, to S₁ and S₂ so as to transmitlight from the light sources to the dichroic mirror 30 disposed at thedistal end of illumination fiber 14. Dichroic mirror 30 can beconfigured to allow light from S₁ to pass substantially straight throughthe mirror while reflecting light from S₂. Collection fibers 38 canreceive light from the illuminated sample (e.g., in the form orscattered, reflected, refracted or fluoresced photons) and transmit thereceived photons to the optical device for imaging and collecting Ramanspectra of the sample. Spectral filter 20 can be disposed between thesample 35 and collection fibers 38 for rejecting light having wavelengthsimilar to S₂. In addition, spatial filter 28 can be disposed betweensample 35 and collection fibers 38 to control the angular field of viewof collection fibers 38.

In FIG. 3A a single dichroic mirror 30 provides the illumination andviewing of forward objects for wavelengths above λ₁ (e.g., NIR). Forilluminating wavelengths below λ₁, the reflection from dichroic mirror30 occurs onto the sample 35. Light scattered, absorbed or emitted fromthe sample 35 from this illumination can be reflected by dichroic mirror30 into the filters 28 and 20 as well as lens 22, the filter 24 and thecollection fiber bundle 38 to the optical analysis and ultimately thedetection system (not show).

FIG. 3B is a schematic representation of another embodiment of thefiberscope's dichroic probe region. The schematic representations ofFIGS. 3A and 3 b utilize discrete optical flats or plates for thedichroic mirror 30, 31 and 32 and window 12. In FIG. 3B several dichroicmirrors 30, 31 and 32 are utilized to enable different illumination andsampling applications. This embodiment also illustrates the flexibilitythat combination of different dichroic mirrors can offer. The dichroicelements at the three different spatial locations can be tailored tooperate at different wavelengths. In one configuration dicrhoic element32 can be removed and a dichroic mirror coating 31 can cover a portionof dichroic mirror 30. Coating 31 can be a dichroic coating that isadopted to be effective for certain wavelengths corresponding to one ormore illumination wavelength (e.g., S₁ and S₂) but not effective forothers (e.g., S₃ to S_(N)). In an alternative embodiment, element 31 maybe a graded dichroic mirror or polychroic mirror having a differentreflection and transmission properties with respect to the wavelengthtransmitted through transmission fibers 14. In still another embodiment,dichroic mirror 30 may be a window to allow viewing under visible light.Alternatively, it may be a dichroic mirror to allow viewing under NIRradiation. Similarly, secondary dichroic mirror 32 can be an additionalmirror or a dichroic mirror depending on the intended application. ForNIR imaging, secondary mirror 32 can be have dichroic surfaces on bothsides to reflect NIR light for viewing/steering and transmits VIS or UVlight for Raman, VIS or Fluorescence spectroscopy.

FIG. 3C is a schematic representation of another embodiment of thefiberscope's dichroic probe region. Particularly, FIG. 3C shows acompound optical element composed of optical material 33 and 34 anddichroic mirror surfaces 31 and 32. Dichroic mirrors 31 and 32 can bemade from the same contiguous material or they can be made from twoseparate segments. In the exemplary embodiment of FIG. 3C, the incidentand scattered radiations are reflected from the same dichroic mirror. Inone embodiment, the forward viewing is optimized by tilting fibers 14downward toward the most extended region of material 33 (not shown) inorder to direct illumination closer to the center of the dichroic mirror30.

The exemplary embodiment represented in FIG. 3C includes compositeoptical material that are fused together to form an internal dichroicmirror surface. The composite optical material include high qualityspectroscopic grade optical material 33, such as, for example quartz,which is highly uniform and lacks defects that may scatter or absorbfluoresce in the UV, VIS, or NIR regions. This allows uniformtransmission of light of wavelengths in a region of interest forspectroscopy or chemical imaging. The composite optical material mayalso include capping material 34 which transmits light having VIS andNIR wavelengths but need not be spectroscopic quality material. Thecapping material 34 may be biocompatible and clearly transmit light inthe VIS and/or NIR thereby enabling visual image formation. Thecomposite structure can function similar to FIG. 3B. The dichroicsurface 31 can provide illumination and viewing of forward objectshaving wavelengths above λ₁ (for example, in the NIR). For illuminatingwavelengths below λ₁, reflection from 31 occurs onto the sample 35.Light scattered, absorbed or emitted from sample 35 may be reflected bythe dichroic mirror surface 32 into filters 22, 24, 28 and lens 36. Thelight is then received by collection fiber 38 and directed to theoptical devices (not shown) for analysis and detection.

One advantage of a compound optical element as shown in FIG. 3C is itssimplicity of fabrication and mounting. For example, the opening at thedistal end of the fiberscope body 10 and the proximal end of compounddichroic element can be tapped so as to snap into the fiberscope bodyhousing 10. The application of a refractive matching fluid atop of thefiberscope window 12 before insertion of the compound lens not onlyprovides a refractive index matched interface but acts as a seal toprohibit bodily fluids from entering this interface. Such a snap-in,composite dichroic lens can be readily replaced in the field.

FIG. 4 is a schematic representation of a dichroic fiberscope probe inan artery according to one embodiment of the disclosure for evaluatingregions in the arterial wall. More specifically, FIG. 4 shows fiberscope40 inside a body lumen (an artery) 41. In the exemplary embodiment ofFIG. 4, fiberscope 40 also includes composite optical element 42 havingdichroic mirror 43. Light having NIR wavelengths (shown as rays 44)originate from source 33 from the composite optical element 42 forilluminating objects in the arterial wall 45. After defining asuspicious area such as plaque 45 or area 46, the head of the fiberscopeand the composite optical element can be positioned at or near sucharea. As shown in FIG. 4, the probe is positioned for detailedspectroscopic examination of target area 46. Once positioned,spectroscopy at a second wavelength can be performed 47 to furtherdiagnose the target area. To minimize the interference from blood andother bodily fluids, an inflatable balloon 48 can be inflated to pushthe composite optical element into the target region so as totemporarily squeeze out residual blood or bodily fluids. Such balloonsare frequently used in cardio vascular devices and can be incorporatedherein to enhance inspection and add functionality. Spectroscopy can beperformed using rays 44 that have been reflected off the dichroic mirror43 onto the target region 46. Scattered, absorbed or fluoresced lightfrom target region 46 is reflected off dichroic mirror 43 into thespectroscopic fibers 38 (see FIG. 3A).

FIG. 54 shows the imaging capabilities of the Raman chemical imagingfiberscope. FIGS. 4A and 4B show a high fidelity image of the exteriorand interior of a bore hole, respectively. These are bright field imagesusing white light illumination which show the video performance of theRaman chemical imaging fiberscope. Overall, the Raman chemical imagingfiberscope has a wide field of view and superb image quality.

The video performance of the Raman chemical imaging fiberscope wasevaluated by recording a digital image of a USAF 1951 resolution target.The target was illuminated with a diffuse Xe arc lamp source. The outputof the Raman chemical imaging fiberscope was optically coupled to acolor CCD video camera and bright field images were digitized using adigital frame grabber. To determine the laser spot position anddimension a diode pumped Nd:YVO₄ laser—doubled to produce 532 nmlight—was injected into the laser delivery fiber. The resultant laserspot was projected onto the resolution target substrate at a nominalworking distance of 1 cm.

FIG. 5 shows resolution target imaged collected through the Ramanchemical imaging fiberscope when back-illuminated with a diffuse Xesource. In FIG. 5A a 532 nm laser beam was focused into the laserdelivery fiber using a high efficiency laser to fiber optic coupler andan image of the laser spot was recorded on a diffuse target superimposed on the resolution target. At a working distance of 1 cm the spotseen near the center of the target image is approximately 2.5 mm indiameter. The laser spot size can be controlled through laser to fiberoptic injection strategies and via working distance to the sample. Forcomparison, FIG. 5B shows the digital image of the USAF resolutiontarget.

As previously described, high performance, environmentally resistantspectral filters can be incorporated into the distal end of the flexibleRaman chemical imaging fiberscope. Room temperature spectra wereacquired to measure the out of band rejection efficiency of thefiberscope using combinations of white light and laser light. Roomtemperature spectra were acquired to measure the 532 nm laser rejectionefficiency during fiberscope collection. Laser rejection is required forthe observation of the weak Raman signal and to prevent the inherentRaman scatter of the collection fiber. Xenon light was sent into thecollection end of the fiberscope. The output from the viewing end of thefiberscope was measured using a dispersive spectrometer.

FIG. 7 shows transmission spectra collected through the Raman chemicalimaging fiberscope. Specifically, FIG. 7A shows the transmissionbandpass through the laser deliver fiber optic under simultaneous Xewhite light and 532 nm laser light illumination. From this spectrum, itis apparent that the incorporated bandpass filter sufficiently passes532 nm light while cutting off transmission above 140 cm⁻¹ red-shiftedfrom the laser line. FIG. 7B shows the transmission bandpass through thefilter incorporated within the coherent fiber bundle. It is apparentthat the incorporated notch filter sufficiently rejects 532 nm lightwhile passing light above 200 cm⁻¹ red-shifted from the laser line.

Dispersive Raman spectra of sodium nitrate and sodium phosphate inaqueous solution collected with the Raman chemical imaging fiberscopeare presented in FIG. 8. The sodium nitrate Raman spectrum in FIG. 8Areveals the characteristic nitrate band at 1065 cm⁻¹. Note the highsignal to background ratio (S/B) and the absence of fiber optic Ramanbackground. In FIG. 8B, the phosphate bands, at 945–995 cm⁻¹ can beseen.

Room temperature Raman spectra of a sodium nitrate pellet was collectedto assess the Raman collection performance of the Raman chemical imagingfiberscope. The viewing end of the fiberscope was coupled to adispersive Raman spectrometer. Illumination of the sodium nitrate pelletwas provided by injecting laser light into the laser delivery fiber.

High temperature Raman spectra of zirconium oxide were also collected. Afurnace was used to heat the sample and digital end of the Ramanchemical imaging fiberscope. A thermocouple was used to monitor thetemperature at the distal end of the fiberscope. A viewing end of thefiberscope was coupled to a dispersive spectrometer. Illumination of thezirconium oxide pellet was provided by injecting laser light into thelaser delivery fiber of the Raman chemical imaging fiberscope.

FIG. 9 shows two zirconium oxide spectra collected (1) at roomtemperature (i.e., 27° C.) and, (2) at the elevated temperature of 205°C. The Raman features are still discernable in the high temperaturespectrum. There is an increase in the overall intensity of thebackground signal (thermal background) and in the relative intensitiesof the peaks. It is noted that both spectra show Raman features to wellwithin 200 cm⁻¹ of the laser line.

Raman chemical image data was collected from an over the counterpharmaceutical tablet containing aspirin (Alka Seltzer from Bayer®Corp.). The image from the viewing end of the fiberscope was focusedonto a CCD camera and an LCTF was inserted into the optical path.Dispersive spectroscopy revealed that the tablet excipient had a Ramanband at 1060 cm⁻¹. Since this is close to the 1044 cm⁻¹ Raman band ofaspirin, these two peaks were used for chemical image analysis. A CCDimage was collected every 9 cm⁻¹ while the LCTF was tuned form 1000 cm⁻¹to 1110 cm⁻¹.

Images of the tablet collected through the fiberscope using ambientlight can be seen in FIGS. 10A and 10B. The box in FIG. 10B shows theregion from where the Raman spectrum in FIG. 10C was acquired. FIG. 10Cshows a dispersive Raman spectrum dominated by aspirin (acetylsalicylicacid). The box shaded in gray represents the spectral range that wassampled to generate Raman chemical images.

The multivariate technique cosine correlation analysis (“CCA”) wasapplied to Raman chemical image data using a ChemImage software. CCA isa multivariate image analysis technique that assesses similarity inchemical image data sets while simultaneously suppressing backgroundeffects when performed in conjunction with normalization of eachlinearly independent Raman spectra contained in the image dataset. CCAassesses chemical heterogeneity without the need for extensive trainingsets. CCA identifies differences in spectral shape and effectivelyprovides molecular-specific contrast that is independent of absoluteintensity.

FIG. 11 displays the Raman chemical imaging results from the aspirintablet. Specifically, FIG. 11A is a bright field image of the sampledarea captured through the Raman chemical imaging fiberscope. FIG. 11B isa grayscale Raman chemical image generated using CCA with the brightestregions showing the aspirin component at 1044 cm⁻¹ and the darkerregions showing the excipient component (calcium carbonate) collected at1060 cm⁻¹. FIG. 11C shows LCTF Raman spectra from regions 1 (localizedaspirin) and 2 (excipient), respectively.

The Raman chemical imaging fiberscope is capable of, among others, thefollowing: laser delivery, white light illumination, video collection,Raman spectral collection and LCTF-based Raman chemical imagingcapability within a compact device (the distal end outside diameter ofthe flexible fiberscope is only 2 mm). The Raman chemical imagingfiberscope is environmental resistant and can be used in a variety ofhostile and confined environments over a range of operating temperaturesand humidity. Due to its compact dimensions and rugged design, the Ramanchemical imaging fiberscope is well suited to in situ industrialmonitoring and in vivo clinical applications.

Although the disclosure has been described in the context of a Ramanfiberscope probe using Raman scattered light, the principles disclosedherein offer the ability to perform other chemical or spectroscopicimaging techniques such as near infrared, fluorescence or luminescencechemical imaging. For example, while Raman measures scattering andprovides molecular based chemical information, absorption of VIS or NIRlight over a range of wavelengths also provides an optical chemicalsignature which can be used to interpret or differentiate the chemicalstate of the sample. Using this fiberscope imaging system such opticalabsorption can be measured by integration over the sample and detectedusing an appropriate spectrometer or imaged to form a UV, NIR or VISabsorption chemical image using an appropriately designed LCTF anddetector. Similarly, light emission arising from, for example,fluorescence can be integrated over the sample and detected with aspectrometer or imaged to form a UV, VIS or NIR emission chemical imageusing an appropriately designed LCTF and detector.

Although the disclosure was described in the context of a Ramanfiberscope probe, the present disclosure offers the ability to performother chemical (spectroscopic) imaging techniques such as near infra-redand luminescence chemical imaging.

The principles of the disclosure have been described in relation toparticular exemplary embodiments which are illustrative not restrictive.Alternative embodiments may become apparent to those skilled in the artto which the present disclosure pertains without departing from theprinciples disclosed herein.

1. A chemical imaging fiberscope for imaging and collecting at least onespectra from a sample comprising: at least one illumination fiber fortransmitting light from a first and a second light source to a distalend of said fiberscope; a dichroic mirror disposed at said distal end ofthe fiberscope such that light from said first light source passessubstantially through said mirror and light of a predeterminedwavelength from said second light source is substantially reflected bysaid mirror toward said sample to thereby illuminate said sample; and atleast one collection fiber for receiving light from said illuminatedsample and transmitting the received light to one or more opticaldevice.
 2. The fiberscope of claim 1 including plural illuminationfibers wherein at least one of said plural illumination fibers transmitslight exclusively from said first light source.
 3. The fiberscope ofclaim 1 further comprising a spectral filter disposed between saidsample and said at least one collection fiber so that said predeterminedwavelength of light from said second light source is rejected.
 4. Thefiberscope of claim 3 wherein said predetermined wavelength isapproximately 670 nanometers.
 5. The fiberscope of claim 3 wherein saidpredetermined wavelength comprises at least one wavelength each of whichis in a range of wavelengths from 220 to 1500 nanometers.
 6. Thefiberscope of claim 3 wherein said predetermined wavelength comprises atleast one wavelength each of which is in a range of wavelengths from 500to 850 nanometers.
 7. The fiberscope of claim 3 wherein saidpredetermined wavelength comprises at least one wavelength each of whichis in a range of wavelengths from 270 to 550 nanometers.
 8. Thefiberscope of claim 1 wherein said second light source is a laser. 9.The fiberscope of claim 1 wherein said first light source is a broadbandnear infrared light source.
 10. The fiberscope of claim 1 wherein saidsecond light source is a broadband near infrared light source.
 11. Thefiberscope of claim 1 wherein said second light source is a broadbandvisible light source.
 12. The fiberscope of claim 1 wherein said secondlight source is a broadband ultraviolet light source.
 13. The fiberscopeof claim 1 including plural illumination fibers wherein one of saidplural illumination fibers transmits light exclusively from said firstlight source and wherein another of said plural illumination fiberstransmits light exclusively from said second light source.
 14. Thefiberscope of claim 1 including a third light source such that said atleast one illumination fiber transmits light from said first, second,and third light sources to said distal end of said fiberscope.
 15. Thefiberscope of claim 14 wherein said first light source is a broadbandnear infrared light source, said second light source is a laser, andsaid third light source is a broadband visible light source.
 16. Thefiberscope of claim 1 wherein the optical device is an opticalspectrometer adapted to be used with one or more of a Raman spectra,VIS/NIR spectra or Fluorescence Spectra.
 17. The fiberscope of claim 1wherein said optical device is a chemical imaging spectrometer anddetector configured to perform chemical imaging for Raman, VIS/NIR andfluorescence.
 18. The fiberscope of claim 1 wherein the light receivedby said at least one collection fiber is scattered from said illuminatedsample.
 19. The fiberscope of claim 1 wherein the light received by saidat least one collection fiber is Raman scattered from said illuminatedsample.
 20. The fiberscope of claim 1 wherein the light received by saidat least one collection fiber is reflected from said illuminated sample.21. The fiberscope of claim 1 wherein the light received by said atleast one collection fiber is fluoresced from said illuminated sample.22. The fiberscope of claim 1 wherein the light received by said atleast one collection fiber has a wavelength in a range of wavelengthsshifted from the illuminating wavelength by −4000 to +4000 wavenumbers(cm⁻¹).
 23. The fiberscope of claim 1 further comprising a spatialfilter disposed between said sample and said at least one collectionfiber for controlling the angular field of view of said at least onecollection fiber.
 24. The fiberscope of claim 1 wherein the opticalproperties of said dichroic mirror are insensitive to temperaturechanges.
 25. The fiberscope of claim 1 wherein the optical properties ofsaid dichroic mirror are insensitive to humidity changes.
 26. Thefiberscope of claim 1 further comprising a lens disposed between saidsample and said at least one collection fiber.
 27. The fiberscope ofclaim 1 further comprising a housing for enclosing said fiberscope. 28.The fiberscope of claim 27 including a window at said distal end of saidfiberscope.
 29. The fiberscope of claim 28 wherein said window issubstantially composed of a material selected from the group consistingof quartz, diamond, sapphire, plastic, glass, and semiconductor.
 30. Thefiberscope of claim 28 wherein said window includes a first portionwhich is spatially patterned for filtering the light from said firstlight source and a second portion which is transparent for the lightfrom said illuminated sample.
 31. The fiberscope of claim 1 including aswitch for alternately connecting either said first or said second lightsource to said at least one illumination fiber, wherein said switchconnects said first light source to said illumination fiber for guidingsaid fiberscope to said sample and wherein said switch connects saidsecond light source to said illumination fiber for illuminating saidsample.
 32. A system for imaging and collecting spectra from a samplecomprising: a near infrared (“NIR”) light source; a laser light source;a fiberscope including: at least one illumination fiber; a dichroicmirror; and at least one collection fiber; and an optical device,wherein said at least one illumination fiber is operatively connected ata proximate end to said NIR light source and said laser light source soas to transmit light from said light sources to said dichroic mirrordisposed in proximity to a distal end of said illumination fiber, andwherein said dichroic mirror allows light from said NIR light source topass substantially straight through said mirror and substantiallyreflects light from said laser light source toward said sample tothereby illuminate said sample, and wherein said at least one collectionfiber receives light from said illuminated sample and transmits thereceived light to said optical device for imaging and collecting thespectra of said sample.
 33. The system of claim 32 further comprising aspectral filter disposed between said sample and said collection fiberfor rejecting light having a wavelength substantially the same as thewavelength of light emitted by said laser light source.
 34. The systemof claim 33 further comprising a spatial filter disposed between saidsample and said collection fiber for controlling the angular field ofview of said collection fiber.
 35. The system of claim 34 furthercomprising a lens disposed between said sample and said collectionfiber.
 36. The system of claim 35 further comprising a housing forenclosing said fiberscope.
 37. The system of claim 36 including a windowat said distal end of said fiberscope.
 38. The system of claim 37wherein said window is substantially composed of a material selectedfrom the group consisting of quartz, diamond, sapphire, plastic, glass,and semiconductor.
 39. The system of claim 37 wherein said windowincludes a first portion which is spatially patterned for filtering thelight from said NIR light source and a second portion which istransparent for the light from said illuminated sample.
 40. The systemof claim 37 including a switch for alternately connecting either saidNIR light source or said laser light source to said illumination fiber,wherein said switch connects said NIR light source to said illuminationfiber for guiding said fiberscope to said sample and wherein said switchconnects said laser light source to said illumination fiber forilluminating said sample.
 41. The system of claim 32 wherein the opticaldevice is an optical spectrometer adapted to be used with one or more ofa Raman spectra, VIS/NIR spectra or Fluorescence Spectra.
 42. The systemof claim 32 wherein said optical device is a chemical imagingspectrometer and detector configured to perform chemical imaging forRaman, VIS/NIR and fluorescence.
 43. The system of claim 32 wherein thelight received by said collection fiber is scattered from saidilluminated sample.
 44. The system of claim 32 wherein the lightreceived by said collection fiber is Raman scattered from saidilluminated sample.
 45. The system of claim 32 wherein the lightreceived by said collection fiber is reflected from said illuminatedsample.
 46. The system of claim 32 wherein the light received by saidcollection fiber is fluoresced from said illuminated sample.
 47. Thesystem of claim 32 wherein the light received by said at least onecollection fiber has a wavelength in a range of wavelengths shifted fromthe illuminating wavelength by −4000 to +4000 wavenumbers (cm⁻¹).
 48. Amethod of imaging and collecting spectra from a sample, the methodcomprising the steps of: providing a fiberscope including: at least oneillumination fiber operatively connected at a proximate end to a firstlight source and a second light source so as to transmit light from saidfirst and second light sources to a dichroic mirror disposed inproximity to a distal end of the fiberscope; at least one collectionfiber for receiving light from said illuminated sample and transmittingthe received light to an optical device; and a dichroic mirror disposedat the distal end of the fiberscope which allows light from the firstlight source to pass substantially straight through the mirror andsubstantially reflects light from the second light source toward thesample to thereby illuminate said sample; guiding the fiberscope usinglight from the first light source; and imaging and collecting spectrafrom the sample using light from the second source.
 49. The method ofclaim 48, wherein the spectra is VIS/NIR.
 50. The method of claim 48,wherein the spectra is fluorescence.
 51. The method of claim 48, whereinthe spectra is Raman.